PDF AN1379 Data sheet ( Hoja de datos )

Número de pieza	AN1379
Descripción	Stopwatch Based on MCP79410 I2C RTCC
Fabricantes	Microchip
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No Preview Available ! AN1379 Stopwatch Based on MCP79410 I2C™ RTCC Author: Eugen Ionescu Microchip Technology Inc. INTRODUCTION The Real-Time Clock/Calendar (RTCC) devices can be successfully used in applications that require very accurate timekeeping. MCP79410 is a feature-rich RTCC that incorporates EEPROM, SRAM, unique ID and time-stamp. FEATURES OF THE RTCC • I2C™ Bus Interface • RTCC with Time/Date Registers: Year, Month, Date, Day of Week, Hours, Minutes, Seconds • Support for Leap Year • Low-power CMOS Technology • Input for External Battery Backup (maintains SRAM, RTCC and timekeeping) • On-board 32,768 kHz Crystal Oscillator for the RTCC FIGURE 1: SCHEMATIC • On-chip Digital Trimming/Calibration of the Oscillator • Operates down to 1.3V VBAT Minimum • Operating Temperature Range: - Industrial (I): -40C to +85C • Multi-function Pin: - Open-drain configuration - Programmable clock frequency out - Programmable alarm output • Interrupt Capability (based on the 2 sets of alarm registers, ALM0 and ALM1) • Time-stamp Registers for holding the Time/Date of Crossing: - from VDD to VBAT - from VBAT to VDD SCHEMATIC The schematic includes a PIC18 Explorer demo board and the I2C RTCC PICtail™ daughter board as shown in Figure 1. LCD LUMEX DB7 - 0 RS E MCP23S17 SPI Expander SCK CS SDI C4 = 0.1 uF C3 32.768 kHz 1 X1 10pF Y C4 R4 BAT 85 1K BAT 2 X2 3 VBAT 100pF 4 VSS RTCC MCP 79410 VDD 8 MFP 7 SCL 6 SDA 5 VDD 2K VDD 2K 2K VDD RC5/SD01 RA2 RA4/T0 CKI PIC18F87J11 RC3/SCK1/SCL1 RC4/SDA1 RB0 RA5 VDD 10K S1 VDD 10K MENU KEY S2 INCR KEY  2011 Microchip Technology Inc. DS01379A-page 1 Free Datasheet http://www.Datasheet4U.com 1 page AN1379 ACCESSING THE RTCC REGISTERS There are two basic functions for accessing the RTCC register: one for writes and one for reads. They can be defined as: void rtcc_wr (unsigned char time_var, unsigned char rtcc_reg), unsigned char rtcc_rd (unsigned char rtcc_reg). Each of these two functions include error messages displayed on LEDs, which could signal when an operation is not acknowledged by the slave (RTCC). EXAMPLE 1: WRITES TO THE RTCC i2c_start() ; // start I2C communication: SDA goes down while SCL remains high i2c_wr(ADDR_RTCC_WRITE); // send the RTCC's address for write = 0xde i2c_wr(rtcc_reg) i2c_wr (time_var) i2c_stop() ; // ; // ; // send the register's address send the data byte stop I2C communication: SDA goes high while SCL remains high EXAMPLE 2: READS FROM THE RTCC i2c_start() ; // start I2C communication: SDA goes down while SCL remains high i2c_wr(ADDR_RTCC_WRITE ; // send the RTCC's address for write = 0xde i2c_wr(rtcc_reg) ; // i2c_restart() ; // i2c_wr(ADDR_RTCC_READ) ; // i2c_rd() ; // send the register's address switch to reads send the RTCC's address for read = 0xdf read the byte from the RTCC (register's content) i2c_nack i2c_stop() ; // ; // NoACK from MCU to the RTCC (no more bytes to read) stop I2C communication: SDA goes high while SCL remains high  2011 Microchip Technology Inc. DS01379A-page 5 Free Datasheet http://www.Datasheet4U.com 5 Page

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